Post by Kiwi on Jul 19, 2011 10:45:40 GMT -4

How and when the location of Tranquility Base was identified is described in an early Apollo 11 book, "First on the Moon - A Voyage with Neil Armstrong, Michael Collins, Edwin E. Aldrin Jr", written with Gene Farmer and Dora Jane Hamblin, epilogue by Arthur C. Clark. Michael Joseph Ltd, London (1970).

Having been published so soon after the landing, recollections of individuals in the book are fresh enough to be reasonably accurate, and with the help of this book and some other sources, listed below, the story goes like this:--

Soon after the Apollo 11 lunar module Eagle touched down on the moon at GET 102:45:40, all that was really known at the Manned Spacecraft Center in Houston was that it had landed long, or downrange, which means it was further west than the planned site. Additonally, the various guidance systems were sending out conflicting information. PNGCS put Eagle a bit north of the planned site, AGS put it in the middle, and the first MSFN report put it to the south.

Staff of the Mapping Sciences Laboratory at the Manned Spacecraft Center pored over enormous enlargements of lunar maps, and as more and more information came in from telemetry and analysis, one big map in the laboratory gradually accumulated a total of 14 round dots which showed estimated landing sites, and they were all within a four- to five-mile radius. Many of the dots were clustered a little west of West Crater, but no one was certain that any of them showed the real site.

It is important to know that it was not critical to the success of the mission to know precisely where Eagle was. Nor was it critical to its later rendezvous with the CSM Columbia. Engineers knew in advance that pinpointing the exact location of the lunar module might be difficult or even impossible, and that in an emergency the ascent stage of Eagle might have to blast off early before the exact location could be ascertained, so they designed the rendezvous system to work with only a rough estimate of the landing site.

There was also another team on the job. This one was an eight-man geological team headed by Dr Eugene M. (Gene) Shoemaker, who worked for the United States Geological Survey. In later years, Gene and his wife Carolyn became world-renowned comet-hunters, and their best-known co-find with colleague David Levy was Comet Shoemaker-Levy 9, which broke into pieces and slammed into Jupiter in July 1994, creating some of the biggest explosions ever observed in our planetary system.

Dr Shoemaker's team was examining its own moon maps in a small science support room at the Manned Spacecraft Center, and also had a direct telephone link to another room in another building, where three more men and a woman from the USGS's Center for Astrogeology in Flagstaff, Arizona, were examining their maps.

There was a difference in how the mapping and geology teams went about their work. The mapping scientists paid attention to incoming telemetry, and the geologists listened for verbal descriptions from the crew. For a while there was not much to go on, but 18 minutes and 15 seconds after the landing, at 103:03:55, Neil Armstrong reported: "The area out the left-hand window is a relatively level plain cratered with a fairly large number of craters of the 5- to 50-foot variety; and some ridges (which are) small, 20, 30 feet high, I would guess; and literally thousands of little, 1- and 2-foot craters around the area..."

Now the the geologists had a clue, and it was Marita West, the only female on the team, who first suggested that the blocky-rimmed crater which Neil had manually flown over, was West Crater.

Shoemaker later explained: "Tracking information indicated that Neil had flown past the middle of the landing ellipse and was several kilometers downrange. We knew that he had flown over a blocky-rim crater, that he had seen rays of ejecta as he passed over, and that the landing pattern had been rather like a fish hook. There were maybe six craters which could fit his description, but once we knew he was downrange we narrowed it to two. I believe that it was Marita West, over in building No. 2, who first suggested that the crater Neil had described was West Crater. All of us came to the same conclusion pretty rapidly."

Four hours after touchdown and more than two hours before the EVA began, the geologists were fairly sure they knew where Eagle was. Having agreed that the crater Neil Armstrong overflew really was West Crater, they settled on a certain point on their map and it proved to be correct within two hundred metres. They translated their guess into lunar longitude and latitude and asked Mission Control to relay the information up to Mike Collins, but for some reason the message was not sent.

Eventually, 151 hours into the mission when Columbia was heading back to earth, the geologists got the final piece of the puzzle. The EVA Capcom, Bruce McCandless, was back on duty and asked some questions about the landing site, about a laser beam from earth that Aldrin and Armstrong had seen after leaving the lunar surface, about the rock samples, and one question about blocky-rimmed craters:

151:33:59 McCandless: Roger. For 64 thousand dollars, we're still trying to work out the location of your landing site, Tranquility Base. We think it is located on LAM-2 chart at Juliet 0.5 and 7.8. Do you still have those charts on board? Over.151:34:24 Collins: Yeah. Stand by one. They're packed.151:34:31 McCandless: Roger. You may not have to unpack it. The position which I just gave you is slightly west of West Crater. I guess it's about two-tenths of a kilometer west of it, and we were wondering if Neil or Buzz had observed any additional landmarks during descent, lunar stay, or ascent which would confirm or disprove this. One thing that we're wondering about is that if you were at this position, you would have seen the Cat's Paw during ascent just up to the north of your track. Over.151:35:18 Armstrong: We were looking for the Cat's Paw, too, thinking we were probably downrange, beyond the Big V. But I think that it's likely that that might have been West Crater that we went across in landing, but - Stand by. [Long pause.]151:36:22 Armstrong: We're hoping, Bruce, that our 16-mm film was working at that point in descent, and we'll be able to confirm our touchdown position. We thought that during ascent we might be able to pick up some recognizable objects close to the landing site, and we did see a number of small craters, and crater rows, and things like that, which we may be able to pick out after the fact, but we haven't been able to yet.

151:36:58 McCandless: Roger. And the next question from our panel is for Buzz. We recall that he reported seeing a laser upon AOS of the Earth the first time after - the first Rev after ascent, and we're wondering what color the beam was and if he could determine at the approximate location with respect to the Earth. Over.151:37:25 Aldrin: It was mostly white, perhaps a tinge of yellowish color to it. And it seemed to be - as I recall it, the terminator of the Earth was toward the horizon and seemed to be about a quarter to a third of the way down from - down towards the terminator of the Earth - from the opposite horizon. That's a third to a quarter Earth radii. Over.151:38:10 McCandless: Roger. And that puts it in the light side? Over.151:38:18 Aldrin: Roger. Yes, it was in the light side. The Earth was about - a two-thirds lit Earth, with the terminator down toward the horizon. And now coming from the opposite limb of the Earth, the sunlight limb, coming down about one-quarter to one-third of a radius in from the limb. Generally, centrally located with respect to a line drawn perpendicular to the terminator that goes through the center. Over.151:38:58 McCandless: Roger, Buzz. We copy.151:39:02 Aldrin: And I got pictures of that. I'm sure that'll show up.151:39:07 Armstrong: And I saw that, too. It was a very bright spot of light and I confirm Buzz's observation of its position.

151:39:15 McCandless: Okay, 11. Very good. Now, with respect to the documented sample container - on television it appeared to us as though the samples for that container were in fact being given - being selected in accordance with some thought or consideration being given to the rocks themselves. And we were wondering if you could give any further details from memory about any of these samples, and the context of the material or the surface from which they were taken. Over.151:39:56 Armstrong: Yes. You remember I initially started on the cut side of the LM that the TV camera was on, and I took a number of samples of rocks on the surface, and several that were just subsurface - about 20 - 15 to 20 feet north of the LM. And then I recalled that that area had been probably swept pretty well by the exhaust of the descent engine, so I crossed over to the southern side of the LM and took a number of samples from the area around the elongate double crater that we commented on and several beyond that and tried to take as many different types - of rock types as I could see by eye, as I could in the short time we had available. There were a number of other samples that I had seen earlier in our stroll around the LM that I had hoped to get back and pick up and put in the documented sample, but I didn't get those and I'll be able to comment in detail when we get in the debriefing session.

151:41:17 McCandless: Roger. Did you observe any small craters with conspicuously blocky rims? Over.151:41:28 Armstrong: Well, aside from the one big one that we went over, I guess there were none in our area. I took a stroll back after putting up the EASEP, and while Buzz was starting to unpack [likely means 'pack up'] the documented sample, took - took a stroll back to a crater behind us that was maybe 70 or 80 feet in diameter and 15 or 20 feet deep, and took some pictures of it. It had rocks in the bottom of pretty good size, considerably bigger than any that were out on the surface, but there was no - we apparently, at 15 feet or so, had not gotten below the regolith. We were essentially showing no bedrock, at least in the walls of the crater at that depth. Over.

That did it! The geologists now had the answer. The crater Armstrong described had no name but it was on the lunar maps, and Eagle's landing site could now be pinpointed beyond a doubt. The crater is now generally referred to as either Little West Crater because of its proximity to West Crater, or as East Crater because it lies to the east of the landing site.

Gene Shoemaker later said, "Had Neil told us about the small crater behind the LM, we could have pinpointed them right then within twelve to twenty meters."

The identification of the exact landing site did not become official until the early morning of 29 July 1969, after the onboard 16mm landing film had been received and processed in the Lunar Receiving Laboratory. The site was stated to be 0 degrees, 41 minutes, 15 seconds north latitude, and 23 degrees, 25 minutes, 45 seconds east longitude. The projected landing site in the flight plan had been 0 degrees, 42 minutes, 50 seconds north latitude, and 23 degrees, 42 minutes, 28 seconds east longitude.

In 1987 the coordinates were refined due to scientists learning more about the moon. The lunar module's location became 0 degrees, 40 minutes, 27 seconds north latitude, and 23 degrees, 28 minutes, 23 seconds east longitude, and the LRRR's location became 0 degrees, 40 minutes, 24 seconds north latitude, and 23 degrees, 28 minutes, 22 seconds east longitude. However, the assignment of lunar latitude and longitude is an evolving process and the figures may change again. Perhaps the most important thing is that the location of the landing spot relative to local landmarks is very accurately known, and Gene Shoemaker and his team got as close as possible to that on 22 July 1969, before the Apollo 11 astronauts returned to earth.

This particular story is only one of perhaps many, so any additions, corrections, and comments are welcome.

Don't criticize what you can't understand. — Bob Dylan, “The Times They Are A-Changin'” (1963)Some people think they are thinking when they are really rearranging their prejudices and superstitions. — Edward R. Murrow (1908–65)

Post by Bob B. on Jul 19, 2011 11:10:02 GMT -4

Four hours after touchdown and more than two hours before the EVA began, the geologists were fairly sure they knew where Eagle was. Having agreed that the crater Neil Armstrong overflew really was West Crater, they settled on a certain point on their map and it proved to be correct within two hundred metres. They translated their guess into lunar longitude and latitude and asked Mission Control to relay the information up to Mike Collins, but for some reason the message was not sent.

According to the communications transcript, the message was sent to Collins; however, it was about 9 1/2 hours after touchdown. They probably mean it wasn't sent immediately when first requested, not that it was never sent at all.